An embodiment of the invention relates to temperature or thermal modeling and thermal management in a handheld multi-function wireless communications device such as a smart phone. Other embodiments are also described.
Consumers' appetite for more performance and functionality from a small form factor, portable computing system such as a handheld wireless communications device (e.g., a smart phone) typically outpaces developments in low power consumption electronics. Thus, manufacturers of such devices are forced to find better ways of coping with high temperature effects (thermals) while trying to maintain a desired performance level for the user. Further, as more functionality and components are packed into a small form factor housing that has limited cooling capacity, the system exhibits “hotspots” or “critical points” inside and/or on the outside surface of the housing, where there is a potential to overheat under certain circumstances (e.g., while the user is playing a video game on his smart phone in hot weather for an extended period of time, a small portion of the rear face of the smart phone may become uncomfortably warm for the user who is holding the phone in his hand).
A closed loop thermal management or control subsystem is typically included in high performance, small form factor computing systems, to manage the thermal behavior of the system so as to avoid thermal issues at suspected critical points. The thermal management subsystem typically includes software (running in the background of the computing system) that gathers temperature data from various temperature sensors embedded in the system in addition to data regarding the current power consumption activity levels in the system. It then processes this data using stored algorithms (that have been determined at the factory) in order to make decisions on whether or not to change any one or more of several power consumption or activity levels in the system that are responsible for heating the system. For instance, the algorithm may indicate that, based on the current input data, one or more proactive measures need to be taken now, in order avoid a potential thermal issue at a given hotspot. The measures may include throttling of a particularly power-hungry component such as an applications processor (e.g., reducing a clock frequency; reducing power supply voltage), activating a cooling fan, and limiting the maximum output power of an audio or RF power amplifier or light source. The algorithm may also work to boost certain activity limits whenever warranted by the input data (e.g., all critical points are cool enough such that cooling fans can remain inactive and all power-hungry components can be allowed to run at their maximum performance level).
A computing system may have several critical points that are located in places where it is difficult to place temperature sensors (e.g., outside surface of a glass panel of a touch screen; outside surface of a back case of a smart phone). Typically, a number of temperature sensors are available, in locations such as on a central processing unit die, in a rotating disk drive unit, on a battery, and near an RF power amplifier. Mathematical thermal modeling techniques have been developed that can estimate the temperature of a target location in a computing system in essentially real-time, based on temperature data coming from integrated sensors in the system that are not at the target location. See for example US Patent Application Publication No. 2010/0094582 of Keith Cox, et al., “Method for Estimating Temperature at a Critical Point”, assigned to the same assignee as the present application (“Our Earlier Application”). A thermal management subsystem relies on such temperature estimates to help it make the right decisions in order to maintain as high a performance limit as possible within various data processing components of the computing system while maintaining the temperature at one or more critical point within a specified set of constraints (e.g., not exceeding any specified critical point temperature limits).
At times it may be desirable to adjust the thermal behavior of a computing system based on the ambient temperature (air temperature outside the housing of the system) during normal or in-the-field use of the system by an end user. For instance, the thermal management system may be designed to actually allow the system to run a little hotter at a higher ambient. This type of adjustment may require knowledge of the ambient temperature. A temperature sensor may be placed at a “cold” spot of the system, to provide a sensed temperature value that is representative of the ambient. However, for a system that has a small form factor such as a smart phone for instance, it may be impossible to find a spot that is not affected by the heat generated inside the system. Another option is to model the ambient temperature (estimate it) based on data from the internal temperature sensors and power sensors, e.g. using the techniques described in Our Earlier Application.